This application is based on and claims priority to Japanese Patent Application No. 2000-163107, filed May 31, 2000, the entire contents of which are hereby expressly incorporated by reference.
1. Field of the Invention
This invention relates to a cowling arrangement for an outboard motor, and more particularly to a cowling arrangement for an outboard motor having a four-cycle engine that includes a variable valve timing mechanism.
2. Description of Related Art
Outboard motors are often powered by internal combustion engines. The engine is typically positioned within an enclosed cowling. The engine is generally vertically arranged, so that a crankshaft thereof may extend downwardly in driving relation with a water propulsion device of the motor, such as a propeller. In order to balance the motor and because of space considerations, the engine is arranged with a crankcase of the engine facing in the direction of a watercraft to which the motor is mounted (i.e., positioned on a front side of the engine), and with the cylinder head positioned on an end of the engine facing away from the watercraft (i.e., positioned on a rear side of the engine).
Air must be supplied to the engine through the cowling for combustion. Conventionally, the cowling is divided into an engine compartment and an air guide chamber, with an air vent in the cowling communicating with the air guide chamber. Outside air is supplied to the engine through the air vent and air guide chamber. In order to prevent the direct entry of water through the air vent into the intake system, the air vent is positioned away from the intake system, typically in the end of the engine facing away from the watercraft.
When water splashes into the air vent, it can flow through the air guide chamber and into the cowling, possibly depositing on engine components. This can result in malfunction of and/or damage to the affected components. In addition, during watercraft turns, any water that pools on the flywheel cover can often drain onto engine components, leading to similar consequences.
Four-cycle internal combustion engines tend to have advantageous emission control and high performance relative to two-cycle internal combustion engines. Accordingly, it is becoming popular for outboard motors to employ such four-cycle internal combustion engines. Typically, the four-cycle engine has intake and exhaust ports, both of which communicate with a combustion chamber. One or more camshafts are often provided to actuate the intake and exhaust valves between an open position and a closed position so that air is introduced into the combustion chamber and exhaust gases are discharged therefrom at proper timing.
Automobile engines often include a variable valve timing mechanism that can advantageously change the opening and closing timing of the valves depending on certain operating conditions, such as engine speed. The intake valve timing usually is advanced at high engine speeds to ensure high charging efficiency and high perfornmance. Intake valve timing usually is delayed at low engine speeds to ensure high combustion efficiency, fuel economy and good emission control.
Sometimes, the variable valve timing mechanism is mounted at the upper end of at least the intake camshaft. This arrangement makes the variable valve timing mechanism especially vulnerable to fouling by water that may enter the cowling through the intake ducts.
A need therefore exists for an improved water preclusion arrangement for an outboard motor having a four-cycle engine with a variable valve timing mechanism, which arrangement provides improved protection of the variable valve timing mechanism from water.
In accordance with one aspect, the present invention provides an outboard motor comprising a cowling and a four-cycle internal combustion engine positioned within the cowling. The cowling has an air intake duct configured to introduce air into the cowling from the environment outside of the cowling. The engine is adapted to drive a substantially vertically oriented crankshaft. The engine comprises a combustion chamber, an induction system configured to supply intake air to the combustion chamber, and an exhaust system configured to conduct combustion products away from the combustion chamber. The induction system is arranged generally on one of a first side of the engine and a second side of the engine, and the exhaust system is arranged generally on the other of the first side and second side of the engine. A camshaft is driven by the crankshaft. A variable valve timing mechanism cooperates with the camshaft and is positioned at an upper end of the camshaft. An engine cover is positioned between an upper end of the engine and the air intake duct. The engine cover has a first upwardly-extending rib positioned between the air intake duct and the first side of the engine, a second upwardly-extending rib positioned between the air intake and a front side of the engine, and an upwardly-extending portion positioned generally above the variable valve timing mechanism. The ribs and upwardly-extending portion are configured to direct air from the air intake duct toward the second side of the engine and away from the variable valve timing mechanism. The air intake duct is positioned offset toward the second side of the engine and generally forwardly of the upwardly-extending portion of the engine cover.
In accordance with another aspect of the present invention, an outboard motor comprises a cowling having an air intake duct configured to introduce air into the cowling from the environment outside of the cowling, and a four-cycle internal combustion engine positioned within the cowling and adapted to drive a substantially vertically oriented crankshaft. A camshaft is arranged generally parallel to the crankshaft. A variable valve timing (VVT) mechanism is configured to selectively vary a phase angle of the camshaft. The VVT mechanism is arranged adjacent an upper end of the camshaft and comprises a setting section, a fluid supply section, and a control section. A cover is arranged between the engine and the air intake. The cover comprises a top portion and a side wall depending from the top portion and having a lower edge. The top portion covers the VVT mechanism, and a portion of the side wall adjacent the VVT mechanism is configured so that the lower edge is at or below a lowermost portion of the VVT mechanism.
In accordance with yet another aspect, the present invention provides an outboard motor comprising a cowling and a four-cycle internal combustion engine positioned within the cowling. The cowling has an air intake duct configured to introduce air into the cowling from the environment outside of the cowling. The engine is adapted to drive a substantially vertically oriented crankshaft. A camshaft is arranged generally parallel to the crankshaft and is driven by the crankshaft. A variable valve timing (VVT) mechanism is configured to selectively vary a phase angle of the camshaft, and is arranged adjacent an upper end of the camshaft. A cover is arranged between the engine and the air intake. The cover comprises a top portion and a side wall depending from the top portion. The air intake duct is positioned on an opposite side of a longitudinal center line of the cowling from the VVT mechanism.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed.